WDPN34 PGTW 121500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (USAGI) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.5N 130.4E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 542 NM NORTHWEST OF YAP
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 27 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM (TS) 27W (USAGI) WITH IMPROVED AND PERSISTENT CONVECTIVE
BANDING WRAPPING AROUND THE LOW-LEVEL CIRCULATION CENTER (LLCC),
PRIMARILY FROM THE WESTERN SEMICIRCLE, THROUGH THE SOUTHERN
QUADRANT, AND INTO THE EASTERN FLANK. ANIMATED WATER VAPOR IMAGERY
HAS ALSO SHOWN MODERATE RADIAL OUTFLOW ALOFT, WITH CIRRIFORM
STRIATIONS THROUGHOUT THE SOUTHWESTERN QUADRANT. THE INITIAL
POSITION IS PLACED WITH MODERATE CONFIDENCE BASED ON EXTRAPOLATION
FROM A 120853Z 91 GHZ SSMIS IMAGE, REVEALING SUSTAINED CONVECTIVE
BANDING WRAPPED AROUND THE LLCC, WITH EVIDENT LOW-LEVEL CURVED
CLOUD LINES INTO THE CENTER. THE INITIAL INTENSITY IS ASSESSED WITH 
MEDIUM CONFIDENCE BASED ON SUBJECTIVE AGENCY ESTIMATES LISTED BELOW, 
WHILE CIMSS OBJECTIVE ESTIMATES RANGE BETWEEN 47 KTS AND 55 KTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTH,
EXTENDING WESTWARD TOWARD TAIWAN.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 55 KTS AT 121016Z
   CIMSS ADT: 47 KTS AT 121130Z
   CIMSS AIDT: 55 KTS AT 121330Z
   CIMSS D-MINT: 54 KTS AT 120858Z
   CIMSS D-PRINT: 54 KTS AT 121330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL STORM 27W IS FORECASTED TO CONTINUE A
NORTHWEST TRACK ALONG THE SOUTHWESTERN PERIPHERY OF THE SUBTROPICAL
RIDGE LOCATED DIRECTLY TO THE NORTHEAST INTO TAU 48. FOLLOWING TAU
48, A BIFURCATION IN MODEL SOLUTIONS HAS ILLUSTRATED TWO POSSIBLE
OUTCOMES FOR 27W, WITH THE JTWC FORECAST SHOWING THE RECURVE
SCENARIO INTO THE LUZON STRAIGHT AND A NORTH-NORTHWEST TRACK INTO
TAU 72. AFTER TAU 72, TS 27W IS EXPECTED TO RECURVE NORTHEASTWARD
THROUGH TAU 120, AHEAD OF AN EXPECTED NORTHEASTERLY COLD SURGE
EVENT. THE SECOND SOLUTION IN THE BIFURCATION SCENARIO ILLUSTRATES
27W AS CONTINUING A TRACK OVER LUZON AT TAU 72, SLOWING IN SPEED
OF APPROACH, AND THEN PROGRESSING WESTWARD TOWARD THE SOUTH CHINA SEA
BY TAU 120. WITH REGARD TO THE INTENSITY FORECAST OF 27W,
INTENSIFICATION IS FORECASTED OVER THE NEXT 48 HOURS, WITH A
MAXIMUM INTENSITY OF 95 KTS. FOLLOWING TAU 48, DRY AIR ENTRAINMENT,
INCREASED VERTICAL WIND SHEAR (VWS) OF GREATER THAN 15 KTS, AND SEA
SURFACE TEMPERATURES OF LESS THAN 26 C ARE EXPECTED TO BEGIN
ERODING USAGI. BY TAU 120, A NON-CONDUCIVE ENVIRONMENT WILL WEAKEN
THE SYSTEM TO AN EXPECTED 30 KTS. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 48 WITH A NORTHWESTWARD TRACK ALONG THE SOUTHWESTERN
PERIPHERY OF THE STR. FOLLOWING TAU 48, A BIFURCATION IN MODEL
SOLUTIONS LENDS LOW CONFIDENCE TO THE FORECAST TRACK INTO TAU 72,
WITH GFS AND NAVGEM TRACKING TS 27W TOWARD THE SOUTH CHINA SEA DUE TO
INFLUENCES FROM THE AFOREMENTIONED COLD SURGE EVENT FROM THE
NORTHEAST. ECMWF AND THE ECMWF ENSEMBLE ILLUSTRATE A RECURVE
SCENARIO TOWARD THE TAIWAN STRAIT. THE JTWC TRACK FORECAST IS
PLACED NEAR THE CONSENSUS INTO TAU 72 AND ALIGNED TO A GREATER EXTENT 
WITH ECMWF THEREAFTER. INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT
INTENSIFICATION WILL OCCUR THROUGH TAU 48 AND BEGIN ITS WEAKENING
PHASE BETWEEN TAU 48 AND TAU 120. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
NNNN